Regarding the holes which indeed often were filled with brass or copper, this was indeed as far as I have known, a talismanic gesture of sorts . This is something often seen on early Arab swords (as seen in Yucel) and seems to have certain corroboration in many early European blades with gold metal filled holes. It would be difficult to draw direct line of influence of course, but there are distinct similarities.
On the spotted corrosion, I also must disclaim any metallurgical skills, but personally have always thought perhaps such anomalies might result from inconsistency in the metals compounded in the blade or impurities pocketed in certain spots.
In another perspective, there have often been somewhat fanciful discussions directed toward blood residue resulting in reactions between the biological components and metals. While not necessarily empirically proven as far as I have known, there is a degree of plausibility. Obviously weapons were typically cleaned after such contact, however if the weapon remained unattended and left in place for a period, perhaps corrosive action might occur over time.
Things to consider
